@Override
 public boolean remove(Object obj) {
   if (!(obj instanceof ObjId)) return false;
   final ObjId id = (ObjId) obj;
   if (!this.isVisible(id.getBytes())) return false;
   return this.tx.delete(id);
 }
 /**
  * Constructor for a single object type.
  *
  * @param tx transaction
  * @param storageId object type storage ID
  */
 ObjTypeSet(Transaction tx, int storageId) {
   super(
       tx,
       FieldTypeRegistry.OBJ_ID,
       true,
       false,
       ByteUtil.EMPTY,
       ObjId.getKeyRange(storageId),
       null,
       new Bounds<ObjId>(ObjId.getMin(storageId), ObjId.getMin(storageId + 1)));
 }